github: support defining handlers for events.
github: support defining handlers for events.

Add two handlers, push and watch


Former-commit-id: 5818b3115887116fe0d65796773da8758dbfc7fb [formerly 53468d22a1dca2e23af70df73024ca96235d03e2]
Former-commit-id: 82f7384c802fed489b8b9e08bbef139b1055b371
torhve/ivar2,torhve/ivar2,torhve/ivar2,haste/ivar2